The present invention relates to a printer, facsimile apparatus, copier or similar ink jet recording apparatus and, more particularly, to an ink jet head for use in an ink jet recording apparatus.
An on-demand type ink jet printer belonging to a family of ink jet recording apparatuses is extensively used because of low cost and relatively high image quality achievable therewith. Various implementations have heretofore been proposed to provide an ink jet head included in such a printer with a compact configuration.
Japanese Patent Laid-Open Publication No. 5-169660, for example, teaches an ink jet head including an actuator portion for transferring energy to ink in a compression chamber, The actuator portion is connected to a drive circuit board, which drives the actuator portion, by flexible wiring, so that a drive portion can be located at the opposite side to the actuator portion Japanese Patent Laid-Open Publication No. 5-50601 proposes an edge type ink jet head and a face type ink jet head each ejecting ink with an electrostatic force. These ink jet heads each has a laminate structure made up of three substrates, i.e., an upper substrate, an intermediate substrate, and a lower substrate. The intermediate substrate is an Si (silicon) substrate formed with nozzle grooves, recesses whose bottoms constitute vibration plates, fine grooves for incoming ink, and recesses constituting ink cavities by photolithography. The upper substrate is formed of glass or plastic and bonded to the intermediate substrate so as to define nozzles, ejection chambers, orifices, and ink cavities. The lower substrate is formed of glass and bonded to the intermediate substrate by anodic bonding so as to form vibration chambers and electrodes respectively corresponding to the vibration plates. A voltage is applied between Si of the intermediate substrate and any one of the electrodes of the lower substrate in order to cause the vibration plate to deform due to an electrostatic force. When the electrostatic force is cancelled, the vibration plate returns to its original position. The resulting increase in pressure inside the ejection chamber causes the ink to be ejected from the nozzle.
Japanese Patent Laid-Open Publication No. 6-71882 proposes a method of reducing a potential difference between the vibration plates and the electrodes at the time of the anodic bonding of the intermediate substrate and lover substrate. The method consists in equalizing the potential of the vibration plates and that of the electrodes by use of a jig. With this method, it is possible to obviate the deformation of the vibration plates ascribable to the above potential difference.
Japanese Patent Laid-Open Publication Nos. 7-125196 and 6-23980 also disclose technologies relating to an ink jet head.
The structure taught in Laid-Open Publication No. 5-169660, however, has some problems left unsolved, as follows. The ejection portion for transferring energy to ink and a drive portion are connected by a flexible printed circuit board (FPC hereinafter), wire bonding, or soldering. This limits the radius of curvature available with the FPC or circuit board for energy transfer and therefore needs a thick support member. Because the electrodes are led out to the rear of the support member, wire bonding, wiring board or soldering is necessary which increase the mounting time and cost. In addition, while Si and a glass substrate are generally bonded together by anodic bonding, it is necessary with a structure of the kind leading out electrodes from the side to dice each piece and then effect anodic bonding or to remove a part of an Si substrate after the anodic bonding of an Si wafer and a glass wafer. Such a procedure is extremely complicated.
The structures-taught in Laid-Open Publication Nos. 5-50601 and 6-71882 each includes terminals for voltage application led out from the surface of the lower substrate by bonding. The precondition with this configuration is that the intermediate and lower substrates be different in dimension. To produce inexpensive heads on a quantity basis, it is necessary that a medium Si substrate and an upper and a lower glass substrate be processed and assembled in a wafer size and then cut into heads In this respect, the above conventional structure is disadvantageous in that steps between the intermediate and lower substrates reduces the number of heads for a single intermediate substrate wafer and thereby increases the cost, and in that a special cutting technique as well as a greater number of times of cutting is necessary. Further, it is almost impossible to equalize the potential of the vibration plates and that of the electrodes with the above implementation when it comes to the wafer size.
Moreover, for color recording, a plurality of heads respectively assigned to different colors of ink must be arranged side by side. Particularly, with the face type head, it is necessary to connect the front of the lower electrodes to the drive circuit by use of, e.g., an FPC. This, however, brings about a problem that because the lower substrate is greater in dimension than the intermediate substrate and because particular portions must be assigned to, eg., an FPC, the overall dimensions of a plurality of heads increase. Another problem is that the limited radius of curvature of the FPC obstructs reliable bonding of the electrodes and FPC. While the nozzles are often arranged in a zigzag configuration in order to increase recording density, such a configuration needs, e.g., two FPCs respectively assigned to two nozzle arrays. As a result, the number of assembling steps and cost are increased.
The structure disclosed in Laid-Open Publication No. 7-125196 has a drawback that the independent electrodes and vibration plates must each be mounted by an exclusive step. Further, electrodes must be led from the independent electrode and vibration plate to the respective mounting regions This, coupled with the fact that the regions assigned to the independent electrodes must extend outward over the regions assigned to the electrodes of the vibration plates, increases the overall size of the substrate.
With the edge type head taught in Laid-Open Publication No. 6-23980 it is difficult to implement multidimensional arrays for mounting reasons. With the face type head, it is easier to implement multidimensional arrays than with the edge type bead; a multistage zigzag arrangement, for example, will increases dot density and therefore resolution. However, even the dot density available with the multistage zigzag arrangement is limited when it is desired to position the mounting surface in the same plane as the nozzles, due to the limited mounting technologies.